When grinding cemented carbide buttons of a drill bit, a grinding cup of the type described above is normally used. The wear part of such grinding cup usually has an abrasive grinding surface that often includes granular diamond. However, the grinding of cemented carbide buttons generates both heat and abrasive cuttings to such an extent that it is necessary to cool the grinding cup and the button bit as well as to flush away the cuttings. The known prior art technique for such cooling is to supply cooling medium, normally water, through the grinding machine and axially through the grinding cup to provide the cooling medium to be discharged in the region where the wear part of the grinding cup engages the free end of the button.
It is previously known through for example International Publication WO 93/25346 to provide a first flush channel which extends centrally through the shank of the grinding cup and which connects to a second flush channel, terminating centrally in a recess in the wear part of the grinding cup.
That recess cannot perform a grinding function and thus leaves a projection in the center of a ground button. The projection may constitute a starting point for a crack in the button when the rock drill bit is reused and thus it may shorten the length of life of the drill bit.
Furthermore it is previously known to provide a groove extending diametrically over the center of the recess, to spread the flushing medium and whereby the available volume of abrasive material is undesirably decreased.